You could try using the online TaxCaster calculator to try out different scenarios.
TurboTax Online is not really suitable for what-if scenarios or sample tax returns. In TurboTax Online there is only one copy of your tax return, and any change you make is saved immediately and permanently. There is no back-out or undo, and no way to exit without saving the changes. If you want to use TurboTax Online to try out different scenarios, you could use a different user ID than the one you use for your actual tax return, but you will have to do a complete new return from scratch. And you have to be careful to keep track of your different user IDs and passwords. TurboTax recommends adding "test" or something similar to the user ID to clearly distinguish it from your actual account.
As xmasbaby0 suggested, the CD or download TurboTax software is much better suited for trying out different scenarios. You can save a copy of your completed tax return with a different file name, then try out the changes in the copy without affecting your actual tax return. The CD/download software also has a What-If Worksheet that lets you easily try out different scenarios using the completed return as a starting point, but without affecting the actual tax return, and it lets you compare the scenarios side-by-side.
